how to sterilize potting soil image

5 Effective Methods for Sterilizing Potting Soil [With & Without Chemicals]

From large-scale farming to backyard gardens, agricultural sciences support the backbone of the world economy. Scientific research continues to grow our understanding of crops and equips us with new ways to take care of our products most efficiently. For example, soil sterilization is an easy technique for even budding gardening enthusiasts to carry out and encourage healthy produce. Before knowing how to sterilize potting soil or dirt, let’s see a brief on sterilizing soil like what it is and why we need to sterile.

What is Sterilized Soil and Why to Sterilize?

Soil sterilization involves chemical or physical processes that are carried out to eliminate the microorganisms living in the soil without harming the produce. It renders the harmful, disease-causing organisms inactive, impotent or unproductive while causing a minimal change in the soil’s chemical and physical composition and provides quick relief to the soil from any factors that may be harming it.

There are a plethora of benefits of disinfecting your soil, some of which are as follows:

  1. It helps create ideal conditions for the growth and development of your plants and promotes yield.
  2. The death of some microorganisms causes the release of nitrates, which are beneficial for plants.
  3. It destroys actively-growing bacteria and resting structures like bacterial spores, which provide prolonged protection and benefit to the plants.
  4. Gardening on the same soil repeatedly without any replenishment can cause a severe depletion in its nutrient composition. Its’ recovery can be aided by carrying out soil sterilization.
  5. By eradicating nutrient competitors like weeds, soil sterilization allows the plant to take up its required nutrients from the soil. This is seen to result in a significant increase in yield.
  6. It helps eliminate the risk of potential disease outbreaks in the soil.
  7. This technique renders the plant toxins soluble, allowing them to wash off.
  8. While it eliminates many bacterial spores, it leaves the thick-walled spores of ammonifying bacteria intact. As they no longer have any competition, ammonia in the soil increases, which is extremely beneficial for plant growth.
  9. It prevents the damping of new seedlings and encourages their healthy growth.

How to Sterilize Potting Soil So Nothing will Grow?

There are various methods of sterilizing potting soil. You can pick the method most convenient to you, keeping in mind a few of the following factors:

  1. The volume of the soil you intend to sterilize.
  2. Materials required to carry out that particular method. If one or more of the necessary tools are not accessible to you, you can easily pick another method that allows you to get the same results with tools already at your disposal.
  3. The amount of labor that method demands. If it requires more time or effort, pick a method that better suits your time commitments.

Things Needed to Sterile Potting Soil at Home

In addition to being advantageous for plant health, soil sterilization also has the added benefit of requiring minimal manual labor and easily available equipment. Some of the tools required are:

  1. Gas grill/oven
  2. Microwave
  3. Roasting pan/baking sheet
  4. Mixing spoon
  5. Meat thermometer
  6. Fertile soil
  7. Aluminum foil/ plastic sheets
  8. Water
  9. Hydrogen peroxide
  10. Formaldehyde

Out of the equipment mentioned above, the articles that come into use will vary depending on which method of soil sterilization you adopt.

5 Great Soil Sterilization Methods

Some methods of sterilization of potting soil listed below:

Method 1: Solarization

solarization image

Solarization, considered to be the best process for the sterilization of garden soil. Normally, beneficial microorganisms survive solarization, and hence it eliminates the concern of diminishing the quality of the soil. It yields the best results when carried out in the summer season, particularly on a dry and sunny day. Preparations for the same should be initiated in the winter by either covering the area with a black plastic sheet or planting some plants to boost soil fertility. In the spring, you must plant new saplings after removing the black sheet.

  • The heat from the sun builds up the temperature of the soil and kills most of the bacteria, weeds, and other disease-causing pests.
  • To sterilize a small quantity of soil, use plastic bags to enclose the soil and create a mini-greenhouse effect when placed in strong sunlight.
  • In the case of larger areas, cover the soil with plastic. This requires strong, direct sunlight to be effective. It is most beneficial to use transparent plastic sheets of adequate thickness, as they allow the suns’ radiation to penetrate the soil directly. However, the very thin sheets can be counter-productive as they heat up very fast and are prone to damage.

Method 2: Microwave Potting Soil Sterilization

soil sterilization in microwave image

This method of baking or sterilizing soil in oven to kill bugs proves useful in cases where we need to process very small amounts of soil. However, this technique may prove to be malodorous; hence the presence of good ventilation is essential. Now, how to sterilize soil in the oven? Simple, you just need to put a small amount, a pint is the recommended amount, of moistened soil in a microwave-safe bag and microwave it on high intensity for 2 minutes and 30 seconds.

Method 3: Sterilizing with Hydrogen Peroxide

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If you want to sterilize soil with chemicals, you can opt this method. Since this technique does not require any technical know-how, it is an excellent choice for new enthusiasts who are still learning their way around a garden. However, utmost caution needs during this method as hydrogen peroxide can cause harm to human skin and has to be adequately diluted before spraying onto the soil. 3% and 35% solutions work well for this technique; though the concentration of the solution determines the exact amount of water to add in each case. After diluting the solution properly, spray it onto the soil. This method works well for both small and large amounts of soil.

Method 4: Sterilizing with Formalin

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This method requires a mix of water and formalin in a very specific ratio of 1 part of 35-40% formalin to 49 parts of water. You must thoroughly soak the soil with this mixture. The recommended amount is approximately 5 gallons of the mix per yard of the soil. It takes about 20 to 40 days for the sterilization to complete, and the soil becomes safe for use. This method proves to be effective against fungal pests, but not against gnats and the like.

Method 5: Steam Sterilization

soil steam sterilization image

In this method, the heat causes the vital cellular proteins of the pests’ bodies to unfold, resulting in their immediate death. This is considered partial disinfection, as the heat-resistant, spore-forming vital bacteria survive the steaming process and enrich and revitalize the soil after it cools down. The steaming should be done at about 180-200 degrees Fahrenheit for 30-45 minutes. This can be done using a pressure cooker; however, while using a pressure cooker, you have to be extremely cautious as the pressure can potentially create an explosive mixture when applied to nitrate-rich soil or manure. This method works great even to sterilize large amounts of soil in the agriculture field.


Does sterilizing soil remove nutrients?

The soil might lost its nutrients, if you sterilize using chemicals. So, try the natural ways like solarization which won’t kill the important microbes. However, you get the nutrients back into the soil by implementing some methods like composting, covering soil with mulch, using permanent paths etc.

How long to bake soil to sterilize?

You need to bake the soil in oven for at least 30 min at 180 to 200 degrees F for sterilization.

Wrapping Up

Though sterilization is not a compulsory procedure in gardening, it is a beneficial process to carry out. It allows you to rest assured regarding the growth and development of your plants by taking a few simple measures. Moreover, it largely eliminates the use of harmful chemicals like weedicides and fungicides, allowing you to raise your plants with the most organic care possible. If you are only facing the problem with weeds, there will be readily available best dandelion killers in the market, with which you can protect your lawn instantly.

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